Patent GB-664068-A (GB)
Title: Improvements relating to television camera cable circuit arrangements
Inventor: WHITE ERIC LAWRENCE CASLING
IPC: H04N5/073
Filed: 1949-03-26
Abstract: 664,068. Television transmitters. ELECTRIC & MUSICAL INDUSTRIES, Ltd. March 14, 1950 [March 26, 1949], No. 8266/49. Class 40 (iii). A television transmitter comprises a camera unit, a control unit therefor, located at a distance from the camera unit, and an electric cable comprising at least two conductors interconnecting the units and fed in balanced fashion with respect to earth with one control signal and in unbalanced fashion with at least one other control signal. In the embodiment described the cable comprises a plurality of conductor pairs, each of which carries a plurality of control signals by means of earth-phantom circuits and/or by circuits capable of discriminating between alternating and direct current signals. A further conductor pair carries signalling current which selectively lights one of two lamps in the camera unit depending upon the polarity of the source at the control unit. In the Figure, the control unit is shown to the left of broken line 1 and the camera unit to the right of broken line 2. Frame-scanning signals are applied from the generator 3 in balanced fashion to conductors 5 and 6 and thence to the scanning coil 8 of the camera tube 4. Frameshift currents from the D.C. source 9 are superimposed on the scanning current. A gammacontrol signal is applied from potentiometer 10 to conductors 5 and 6 arranged as an earthphantom and taken off at the camera unit to the video amplifier 11 through filter circuit 18, 19, 68. Frame-frequency black-out pulses from circuit 16 are applied via conductors 5 and 6 arranged as an earth phantom and filter circuit 20, 21, 22 to suppression-waveform generator 23, which applies appropriate blanking signals to the amplifier 11. Referring to conductorpair 24, 25, frame-scanning signals from generator 28 are applied by a balanced circuit including these conductors to the framescanning coil 26 of a monitor-receiving cathoderay tube 27. A variable resistor 43 in parallel with coil 26 controls the frame-scan amplitude. Line-synchronizing signals from generator 30 and line-scan-amplitude-control signals from potentiometer 39 are applied by an earthphantom circuit including conductors 24, 25 to suppression-waveform generator 23 and linescan generator 38 and to line-scan generator 38 respectively, the latter signal controlling the width of the scanning raster produced upon the camera tube 4. A further circuit comprising balanced conductors 44, 45 conveys telephone signals from microphone 46 to head-phones 50. Conductor 44 also carries a D.C. gain-control signal from potentiometer 54 to amplifier 11 and conductor 45 conveys a focusing-control signal from potentiometer 56 to integrating circuit 57, 58 and thence by means not shown to the camera tube. A further circuit comprises conductors 60, 61, a two-way-and-off switch 62 to which conductor 60 is connected and a potential source 63 to the mid-point of which conductor 61 is connected. At the camera unit, the circuit comprises two lamps 64, 65 in series respectively with rectifiers 66, 67 which are so poled that the lamps light selectively in response to the direction in which switch 62 is closed. The lamps may be replaced by other signalling means, e.g. buzzers or relays.